United States
Environmental Protection
Agency
Office of Prevention, Pesticides
And Toxic Substances
(H-7508W)
EPA-738-F-94-014
September 1994
R.E.D. FACTS
Difenzoquat
Pesticide
Registration
Use Profile
Regulatory
History
All pesticides sold or distributed in the United States must be
registered by EPA, based on scientific studies showing that they can be used
without posing unreasonable risks to people or the environment. Because of
advances in scientific knowledge, the law requires that pesticides which
were first registered years ago be reregistered to ensure that they meet
today's more stringent standards.
In evaluating pesticides for reregistration, EPA obtains and reviews a
complete set of studies from pesticide producers, describing the human
health and environmental effects of each pesticide. The Agency imposes
any regulatory controls that are needed to effectively manage each
pesticide's risks. EPA then reregisters pesticides that can be used without
posing unreasonable risks to human health or the environment.
When a pesticide is eligible for reregistration, EPA announces this and
explains why in a Reregistration Eligibility Decision (RED) document. This
fact sheet summarizes the information in the RED for reregistration Case
0223, difenzoquat.
Difenzoquat is a selective, post-emergent herbicide used to control
wild oats in barley and wheat. Wild oats is an annual grassy weed that out-
competes barley and wheat, causing serious yield losses. Marketed under
the trade name Avenge, difenzoquat is a soluble concentrate/liquid applied
once per growing season as a ground or aerial broadcast treatment. Most of
the product used in the U.S. is applied to wheat crops (64-77%).
Difenzoquat was first registered as a pesticide in the U.S. in July
1975, for its current uses. EPA issued a Registration Standard for
difenzoquat in December 1988 (NTIS #PB89-162127). Currently, two
difenzoquat pesticide products are registered. One is a technical grade,
manufacturing use product containing 96% of the active ingredient; the
other is the end-use product Avenge, a soluble concentrate containing
31.2% active ingredient.
Human Health Toxicity
Assessment In acute toxicity studies, difenzoquat has caused severe irritation to the
eyes of rabbits. It has been placed in Toxicity Category I, indicating the
greatest degree of acute toxicity, for eye irritation effects. Difenzoquat
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causes a moderate degree of acute toxicity administered orally, to the skin
and by inhalation, and has been placed in Toxicity Categories II and III for
these effects.
In a subchronic feeding study using beagle dogs, difenzoquat caused
no treatment-related effects. However, treatment-related skin reactions and
effects were noted in a dermal toxicity study using rabbits.
A chronic toxicity study using rats resulted only in decreased body
weight gains. A study using beagle dogs resulted in numerous toxic signs
including high mortality, decreased food consumption, weight loss, tremors,
lethargy and irregular gait. Difenzoquat is not carcinogenic in studies using
rats and mice, and has been classified as a Group E carcinogen (a compound
showing evidence of non-carcinogenicity for humans).
Developmental toxicity studies using rats and rabbits resulted in
maternal toxicity in the higher dose groups, a decrease in fetal weights in
rats, and vertebrae abnormalities in rabbit offspring. In a reproductive
toxicity study using rats, difenzoquat caused maternal decreased body
weight gain and weight decreases in pups at birth and weaning. Difenzoquat
is not mutagenic. Neurotoxicity studies still are required.
Dietary Exposure
People may be exposed to low level residues of difenzoquat in the diet
when consuming wheat, barley or the meat of poultry, cattle, hogs and
sheep. Tolerances or maximum residue limits are established, and have
been reassessed, for residues of difenzoquat in barley and wheat grain and
straw, in the meat, fat and byproducts of cattle, goats, hogs, horses and
sheep, and in poultry meat and meat byproducts (please see 40 CFR
180.369). Tolerances are not established or needed for milk or eggs, but
food and feed additive tolerances must be established for wheat bran and
shorts, and barley bran and hulls.
EPA estimates that the overall U.S. population is exposed to about
0.1% of the difenzoquat Reference Dose (RfD), or amount believed not to
cause adverse effects if consumed daily over a 70-year lifetime. Children
aged one through six, the most highly exposed population subgroup, are
exposed to about 0.2% of the RfD. The new food additive tolerance for
wheat bran will not cause a measurable increase in these extremely low
exposure levels.
Occupational and Residential Exposure
Pesticide handlers (mixers, loaders and applicators) may be exposed to
difenzoquat during application. However, difenzoquat generally is of low
acute toxicity and causes no toxicity concerns for workers, with the
exception of primary eye irritation. Since difenzoquat is extremely acutely
toxic to the eyes and is placed in Toxicity Category I for eye irritation, a 48
hour restricted entry interval (REI) imposed by the Worker Protection
Standard (WPS) will be maintained. During this time period, workers who
must enter treated areas will be required to wear personal protective
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Environmental
Assessment
Additional Data
Required
equipment (PPE) including coveralls, chemical-resistant gloves, shoes plus
socks, and protective eyewear.
Human Risk Assessment
Although difenzoquat is used on barley and wheat crops, consumers
are exposed to extremely low level residues in their diets posing no known
risks. Difenzoquat generally is of low acute toxicity but poses a risk of
acute eye irritation to workers. To mitigate this risk, a 48 hour restricted
entry interval will be maintained. People who must enter treated areas
during this time are required to wear designated protective clothing and
equipment including protective eyewear.
Environmental Fate
Difenzoquat is persistent and relatively immobile. However, the
environmental fate assessment is not complete because the route of
dissipation has not been established. Laboratory data indicate that
difenzoquat binds with/is immobile in soil and has little potential for ground
water contamination. However, field dissipation studies contrast sharply
and indicate that residues decline with time. Additional, confirmatory data
are required to compare the recovery methods used in laboratory and field
studies.
Ecological Effects
Difenzoquat is slightly toxic to practically non-toxic to birds and
freshwater fish, but is moderately toxic to freshwater invertebrates. It is
non-toxic to honey bees.
Ecological Effects Risk Assessment
Current uses of difenzoquat do not pose any unreasonable threat to the
environment. Difenzoquat is believed to present a slight to moderate
potential for acute toxicity to wildlife and aquatic species. Actual acute
risks, however, appear to be minimal. Chronic toxicity to wildlife appears
to be slight, and chronic risk to fish is unlikely.
Since difenzoquat is a herbicide that is applied aerially, risk to non-
target aquatic and terrestrial plants, including endangered plant species, is
expected to be high. Additional, confirmatory data are required to assess
these risks. In addition, EPA is exploring risk mitigation for all herbicides.
EPA is requiring the following generic data for difenzoquat to confirm
its regulatory assessments and conclusions:
Acute and 90-Day Neurotoxicity Screening Studies;
Seed Germination/Seedling Emergence;
Vegetative Vigor;
Aquatic Plant Growth;
Confined Rotational Crop;
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Product Labeling
Changes Required
Regulatory
Conclusion
For More
Information
Droplet Size Spectrum;
Drift Field Evaluation;
Non-guideline laboratory study comparing recovery methods used in
previous laboratory and field dissipation studies.
The Agency also is requiring product-specific data including product
chemistry and acute toxicity studies, revised Confidential Statements of
Formula (CSF) and revised labeling for reregistration.
The labels of all registered pesticide products containing difenzoquat
must comply with EPA's current pesticide labeling requirements. No
additional labeling requirements are required for the end-use product at this
time. However:
• The Restricted Entry Interval (REI) established by the Worker
Protection Standard must remain at 48 hours. This REI must be inserted
into the standardized REI statement required by PR Notice 93-7.
• Personal protective equipment (PPE) for early entry includes
coveralls, chemical resistant gloves, shoes plus socks, and protective
eyewear. These items must be inserted into the early entry PPE statement
required by PR Notice 93-7.
The use of currently registered pesticide products containing
difenzoquat in accordance with approved labeling will not pose unreasonable
risks or adverse effects to humans or the environment. Therefore, all uses
of these products are eligible for reregistration.
These difenzoquat products will be reregistered once the confirmatory
generic data, product specific data, revised Confidential Statements of
Formula and revised labeling are received and accepted by EPA.
EPA is requesting public comments on the Reregistration Eligibility
Decision (RED) document for difenzoquat during a 60-day time period, as
announced in a Notice of Availability published in the Federal Register. To
obtain a copy of the RED document or to submit written comments, please
contact the Pesticide Docket, Public Response and Program Resources
Branch, Field Operations Division (7506C), Office of Pesticide Programs
(OPP), US EPA, Washington, DC 20460, telephone 703-305-5805.
Following the comment period, the difenzoquat RED document will
be available from the National Technical Information Service (NTIS), 5285
Port Royal Road, Springfield, VA 22161, telephone 703-487-4650.
For more information about EPA's pesticide reregistration program,
the difenzoquat RED, or reregistration of individual products containing
difenzoquat, please contact the Special Review and Reregistration Division
(7508W), OPP, US EPA, Washington, DC 20460, telephone 703-308-8000.
For information about the health effects of pesticides, or for assistance
in recognizing and managing pesticide poisoning symptoms, please contact
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the National Pesticides Telecommunications Network (NPTN). Call toll-
free 1-800-858-7378, between 8:00 am and 6:00 pm Central Time, Monday
- Friday.
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